Great, now how can I use it?

You could run this from the console window by typing gulp javascript but we are using Visual Studio and have this fancy Task Runner Explorer we want to use. If you already had the Task Runner Explorer open you may have seen it change from this

Before

to this

After

when we created the javascript task.

If you did not go to your View -> Other Windows -> Task Runner Explorer to open it.

Now you can see all the tasks you currently have set up, in this case just the one. To run it, right click and select run or double click it. This will open a window to the right of the available tasks and show the console output of the task you ran.

If you are following along at home you should now have a file in your wwwroot named app.js that looks like this.